1. Technical Field
The invention relates to a multispindle thread cutter apparatus, having a drive shaft to be driven by motor, having a plurality of work spindles disposed side by side, each of which can be equipped with a thread cutting tool, and having a distributor and reversing gear interposed between the drive shaft and the work spindles, by way of which gear the work spindles are driven to rotate by the drive shaft, and which has an indexable reversing coupling device, with which the directions of rotation of the work spindles can be reversed while the drive shaft continues to rotate in the same direction uninterruptedly, in that two gear wheels, driven to rotate in opposite directions by the drive shaft, are coupled in alternation to the work spindles.
2. Prior Art
One such multispindle thread cutter apparatus is disclosed by German Patent 547 060. It includes two centrally disposed gear wheels, which rotate in opposite directions continuously during operation, because one meshes directly, and the other indirectly via an intermediate wheel, with the drive shaft driven by a drive motor. A coupling disk provided with a toothed ring can be shifted between two indexing positions, in which it enters alternatingly into a rotary drive connection with one of the two gear wheels. Distributed along the circumference of the toothed ring are a plurality of driven gear wheels that engage it, and that are each connected to one work spindle to which a thread tap can be affixed. The instantaneous direction of rotation of the work spindles depends on the indexing position of the coupling disk, which in turn depends on the axial position of the work spindles, which shift axially during the thread cutting process relative to the housing that receives the distributor and reversing gear.
The distributor and reversing gear of the known apparatus is exposed to heavy loads, particularly in the region of the reversing coupling device that contains the coupling disk. This sets an upper limit on the number of work spindles present, and this limit is lower, the greater the forces that arise in the individual thread cutting processes. But even if the number of work spindles is kept reduced, nevertheless premature wear, which makes replacement of the affected parts unavoidable, must be expected in the region of the friction-locking connections between the coupling disk and a given gear wheel.
Admittedly problems in the region of the reversing coupling device can be circumvented by omitting such an reversing coupling device completely. Corresponding arrangements are disclosed in the journal "Werkstatt und Betrieb" [Factory and Shop], Vol. 101, 1968, No. 11, page 705, or from the journal "TZ f. prakt. Metallbearb." [Technical Journal for Practical Metal Machining], Vol. 16, 1966, No. 4, pp. 247/248. In such arrangements, however, the thread cutting process necessarily requires reversing of the drive shaft in order to switchover between counterclockwise and clockwise rotation. Thus the drive mechanism requires special provisions, which make its design and the thread cutting process relatively complicated and expensive.
In a multispindle thread cutter apparatus known from U.S. Pat. No. 2,615,183, a nonreversing operation of the drive shaft is possible, and the reversing coupling device that is present promises a greater capacity to withstand heavy loads, since in each case a form-locking coupling engagement can be made. However, because of the heavy load, not-insignificant wear might occur, especially in the switchover processes, which makes it appear wise to shut down the apparatus prematurely during the switchover process.